Production method and production device for tube with spirally grooved inner surface

ABSTRACT

A method in accordance with the present application includes sending a raw tube from a drum to an unwinding side capstan while the raw tube is rotated around a central axis perpendicular to a winding shaft of the drum by rotating the drum and the unwinding side capstan about the central axis concurrently with unwinding of the raw tube from the drum holding the raw tube, on an inner surface of which multiple straight grooves along a longitudinal direction of the raw tube are formed with an interval in a circumferential direction, in a coil shape, to wind the raw tube around the unwinding side capstan, and drawing in which the unwound raw tube is drawn while the diameter of the raw tube is reduced, and then the raw tube is wound around the drawing side capstan to twist the raw tube and obtain an inner spiral grooved tube.

This application is a division of U.S. application Ser. No. 15/810,785filed Nov. 13, 2017, which is a division of U.S. application Ser. No.15/326,286 filed Jan. 13, 2017 (now U.S. Pat. No. 9,833,825), which is a371 of International Application No. PCT/JP2015/070412 filed Jul. 16,2015, and claims the benefit of priority from Japanese PatentApplication No. 2014-148340 filed Jul. 18, 2014, the entire contents ofeach of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a method of producing an inner spiralgrooved tube used for a heat transfer tube of a heat exchanger and anapparatus for producing the inner spiral grooved tube.

BACKGROUND ART

In the fin tube type heat exchangers such as air conditioners and waterheaters, heat exchange is performed by inserting the heat transfer tube,which is for passing refrigerant in the aluminum fin material, into thefin tube type heat exchanger. Conventionally, copper tubes have beenused as the heat transfer tube. However, due to the demands for weightsaving, cost reduction, and improved recyclability, there is a need forsubstituting the copper tubes with aluminum alloy tubes.

Recently, improvement of the heat-transfer property is attempted in airconditioners for energy saving; and re-examining the kind of therefrigerant and improvement of the structural design of the heatexchanger are made. Under the circumstance, there is a demand for a heattransfer tube, which is one of components of the heat exchanger, havingan even higher performance. Currently, inner grooved tubes, on the innersurface of which continuous spiral grooves are provided, are mainly usedto improve the heat-transfer property.

As a method of producing an inner spiral grooved tube, a groove rollingmethod, in which a tube is drawn while spiral grooves are rolled in theinner surface of the tube, is known (Patent Literature 1 (PTL 1)). Inthe groove rolling method for the conventional copper tubes, spiralgrooves are rolled on the inner surface of the tube by pressing the tubeon a grooved plug, which is provided in the inner circumference of thetube, from the outer circumference of the tube by using a ball bearingrotating at a high speed. Similar groove rolling methods are planned tobe used for producing an inner spiral grooved tube made of aluminum oraluminum alloy.

As an alternative method of producing an inner spiral grooved tube, amethod, in which an inner spiral grooved tube with an twist angle isproduced by: using a raw tube having straight grooves on the innersurface; and drawing the tube with a drawing die while the diameter ofthe tube is reduced with the drawing die concurrently with twisting theraw tube in front of the drawing die to form plastic flow in the reduceddiameter portion of the raw tube, is known (Patent Literature 2 (PTL2)).

As another alternative method of producing an inner spiral grooved tube,a method, in which an inner spiral grooved tube is produced by: windinga raw tube, on the inner surface of which straight grooves along alongitudinal direction of the raw tube are formed with an interval inthe circumferential direction, in a coiled shape; and stretching thecoiled shape raw tube in a straight tubeshape by applying a constanttension along the axis of the coil to introduce twist in the raw tube,is known (Patent Literature 3 (PTL 3)).

CITATION LIST Patent Literature

PTL 1: Japanese Unexamined Patent Application, First Publication No.106-190476 (A)

PTL 2: Japanese Unexamined Patent Application, First Publication No.H10-166086 (A)

PTL 3: Japanese Unexamined Patent Application, First Publication No.2012-236225 (A)

SUMMARY OF INVENTION Technical Problem

However, in producing an inner spiral grooved tube made of aluminumalloy, it is difficult to obtain a predetermined groove shape in thegroove rolling method disclosed in PTL 1. Aluminum alloy has a lowerstrength than that of copper alloy. Thus, in order to obtain asufficient pressure capacity of the inner spiral grooved tube, it isnecessary for the bottom wall thickness of the tube to be thicker thanthat of the inner spiral grooved tube made of copper alloy. In thiscase, since plastic flow is difficult to be formed, rolling apredetermined inner groove shape, particularly so called “the high slimtype fin” having a high fin height and a narrow fin width, is difficult.Thus, defects due to improper plastic flow, such as missing groove andthe like, are likely to be formed. When the tube is processed forcedly,it buckles or ruptures. In addition, aluminum chip is formed by thegrooved plug, which is provided in the inner circumference side of thetube, contacting on the inner circumference side of the tube. Due toaluminum chip formation, the accuracy of the groove shape duringprocessing is reduced. In addition, the aluminum chip resides in thetube to clog a groove since it is difficult to remove it after theprocessing. Thus, there are problems having deteriorated heat-transferproperty and increased pressure loss in the method disclosed in PTL 1.Furthermore, in the groove rolling method, variation in the groove shapeis large. This is because of filling the inner circumference side of thetube with lubricant for groove rolling during inserting the floatingplug in advance. The viscosity of the lubricant deteriorates and isreduced in processing for a long distance in the longitudinal directionof the coil. It causes differences of the bottom wall thickness and thegroove shape of the produced inner spiral grooved tube between the headand the tail of the tube in the longitudinal direction. The variationsin the bottom wall thickness and the groove shape effect onheat-transfer property. At the same time, they cause formation ofvariation in the tube expansion rate in an expanded tube for joining thefin and the inner spiral grooved tube.

Because of this, an alternative method other than this groove rollingmethod is needed for producing the inner spiral grooved tube made ofaluminum alloy.

The production apparatus described in the above-mentioned PTL 2 has theconfiguration, in which the dispensing drum 102 is journaled by therotation shaft 101 supported rotatably about the shaft and horizontallyby the pair of columnar support parts 100; and the raw tube 103 is woundaround the winding drum 106 after the raw tube 103 having been woundaround the dispensing drum 102 in the coiled shape is drawn through thedrawing die 105 as shown in FIG. 14.

On the inner surface of the raw tube 103, multiple straight grooves areformed; and the raw tube 103 having passed the drawing die 105 is shapedinto the inner spiral grooved tube 108 having the spiral grooves on theinner surface.

In FIG. 14, the part 110 is a drive unit such as a motor or the like forrotating the rotation shaft 101. The output shaft of this drive unit 110transmits rotational driving force to the rear end side of the rotationshaft 101 through the transmission part 111 such as the endless belt orthe like. The drawing shown in FIG. 14 is a simplified one. The rotationshaft is constituted as a part of a frame; and the dispensing drum 102is rotatably supported by the rotation axis 113 in the inside of theframe. On the front end side of the rotation shaft 101, a roller, whichguides the raw tube 103 and is not depicted in the drawing, is provided.Through this roller, the traveling track of the raw tube 103 is changed;and the raw tube 103 can be drawn after performing axis alignment of theraw tube 103 to the drawing hole of the drawing die 105 provided on thetable 115.

The production apparatus shown in FIG. 14 is known as an apparatuscapable of producing an inner spiral grooved tube with a large twistangle by reducing the diameter of the tube while the raw tube is twistedwith the drawing die 105 to form plastic flow in the reduced diameterpart of the raw tube 103. However, buckling occurs on the raw tube 103due to the action of twisting in the midstream: from the location, inwhich the raw tube 103 is dispensed from the dispensing drum 102; to thelocation reaching to the drawing die 105 in the production apparatusshown in FIG. 14. Thus, it is difficult to introduce a large twistangle. In other words, it has been difficult to balance actions of bothforces of: twisting; and reducing the diameter of the tube, in theinside of the drawing die 105 properly. Because of this, the apparatushas a problem that torsional force is concentrated in the interposingpart: from the location the raw tube 103 is dispense from the dispensingdrum 102; to the location reaching to the drawing die 105, such as thelocation of the front end side of the rotation shaft 101 where thetraveling track of the raw tube 103 is changed, the location in front ofor after the above-mentioned location, and the like, for the raw tube103 to be buckled easily before reaching to the die 105.

The production apparatus described in the above-mentioned PTL 3 is anapparatus of producing an inner spiral grooved tube having spiralgrooves on the inner surface by forming a constant twist in an extrudedtube, on the inner surface of which multiple straight grooves along thelongitudinal direction of the raw tube are formed with an interval inthe circumferential direction. The outline of the apparatus is shown inFIG. 16.

The production apparatus 120 shown in FIG. 16 includes: the winding part123 winding the extruded raw tube 121, on the inner surface of whichinner fins are formed by multiple straight grooves, on the circumferenceof the winding roll 122 in a coiled shape; the stretching part 130stretching the coiled tube material 121 a formed in the coiled shape inthe extending direction toward the foreside of the coil axis 124 toshape it into a straight tube form; the drawing die, which corrects thesectional shape of the tube body after stretching and is not depicted inthe drawing; and the heat treatment part heating the inner spiralgrooved tube after correcting. Multiple stages of the productionapparatuses 120 shown in FIG. 16 are used series-connected depending onthe extent of the twist angle needed.

In the production apparatus 120, the feed roll 125, which feed thecoiled tube material 121 a to the outside of the winding roll 122 andthe presser roll 126 are provided; and the guide plate 127 restrictingthe coiled tube material 121 a is provided. A heater is built in a partof the presser roll 126; and the coiled tube material 121 a can beheated to the temperature needed for processing (200° C. to 300° C.).

To the stretching part 130, the stretcher 128, which stretches thecoiled tube material 121 a by chucking, and multiple pinch controls,which shape the stretched tube material into a straight tubeshape whiletension is placed on the tube material, are provided. After theprocessing, the inner spiral grooved tube 132 is wound around thewinding roll 131

The extruded raw tube 121 having straight grooves on the inner surfaceis processed to be an inner spiral grooved tube 132 having spiralgrooves on the inner surface and can be wound up by: processing theextruded raw tube 121 made of aluminum or aluminum alloy into the coiledtube material 121 a; and stretching with the stretcher 128; and shapingthe stretched tube material into a straight tubeshape by the pinch rolls129, using the production apparatus 120 shown in FIG. 16,

However, when the inner spiral grooved tube is produced by theproduction apparatus 120 shown in FIG. 16, the twist angle obtaineddepends on the diameter of the winding roll 122. Thus, when it is neededto obtain a large twist angle in a single processing, the diameter hasto be small. However, a hollow tube is wound around a roll with a smalldiameter, it is possible that the tube is flattened or buckled. Thus, aprocess of winding around a roll with a large diameter and stretchingthe coiled tube material has to be repeated multiple times; and it isnot productive. In addition, it has a problem that the production timebecomes longer due to necessity of heat treatment process for removal ofwork-hardening since the tube work-hardens in the process for windingaround the roll and the process for stretching.

In addition, not only the diameter of the roll for winding but also thepitch in being wound in the coiled shape significantly effects on thetwist angle introduce as described above. However, processing a tube ina spring shape with a constant pitch is difficult. As a result,producing an inner spiral grooved tube by using the production apparatus120 shown in FIG. 16 has a problem that there is large variety in thetwist angle in the longitudinal direction of the tube; and a consistenttwist angle cannot be introduced in the tube. Moreover, by repeating theabove-described process multiple times, the variation of the twist angleis likely to be even larger.

The present invention is made under the circumstance described above.The purpose of the present invention is to provide a method of producingan inner spiral grooved tube and an apparatus for producing an innerspiral grooved tube, in each of which there is no formation of aluminumchip on the inner circumference in producing the inner spiral groovedtube; the dimensional accuracies of the groove shape and the twist angleare high in the longitudinal direction; an inner spiral grooved tubewith a high height of fins is obtained; a large twist angle can beintroduced; and productivity is high.

Solution to Problem

An aspect of the present invention is a method for producing an innerspiral grooved tube including the steps of: unwinding a raw tube from adrum to an unwinding side capstan while the raw tube is rotated around acentral axis perpendicular to a winding shaft of the drum by rotatingthe drum and the unwinding side capstan about the central axisconcurrently with unwinding of the raw tube from the drum holding theraw tube, on an inner surface of which multiple straight grooves along alongitudinal direction of the raw tube are formed with an interval in acircumferential direction, in a coil shape, to wind the raw tube aroundthe unwinding side capstan; and twisting and drawing the unwound rawtube by introducing twist to the unwound raw tube while a diameter ofthe unwound raw tube is reduced by being passed through a drawing die,to obtain an inner spiral grooved tube.

By simply feeding the raw tube from the coil and passing it through thedrawing die as it is as disclosed in the method disclosed in PTL 2, thedistance of the processing zone of the raw tube unwound from the coilentering in the drawing die is long. Thus, kink is formed in such a waythat the raw tube is locally bent in the interposing part; and bucklingis likely to occur on the raw tube. Therefore, a large twist cannot beintroduced in the method disclosed in PTL 2.

When an inner spiral grooved tube is produced by the method of producingan inner spiral grooved tube, which is an aspect of the presentinvention, the raw tube is wound around the unwinding side capstan infront of the drawing die; and the unwinding side capstan is rotatedsynchronizing to the rotation of the unwound side drum. Thus, thecentral axis of the processing zone introducing twist can be displacedfrom the unwinding track of the raw tube from the unwound side drum inthe direction parallel to the rotation axis of the capstan to the extentcorresponding to the number of turns of the tube wound around thecapstan. In addition, the distance of the processing zone twisting theraw tube is set from the top location of the unwinding side capstan tothe terminal end portion of the drawing die, and can be controlled to aconstant value within a range of shorter values by the raw tube beingwound around and held on the capstan. Therefore, a constant twist anglecan be stably introduced in the longitudinal direction of the raw tubeby controlling the unwinding speed of the raw tube and the rotationspeed (revolution means the rotation of the unwinding side capstan aboutthe axis of the processing zone) of the unwinding side capstan; and thediameter reduction ratio in drawing. At the same time, occurrence ofbuckling can be suppressed even in introducing a large twist angle inthe process of a single unwinding by: adjusting the distance from thecapstan in front of the drawing die to the drawing die to set thedistance between them to be relatively short; and setting the diameterreduction ratio to a high value.

In addition, if there were a function introducing backward tension tothe rotation of the drum with a brake device such as the powder brakeand the like; and a function introducing forward tension to the rotationof the drum by providing the drawing side capstan, in unwinding the rawtube from the drum, appropriate tension could be stably introduced inthe raw tube. Thus, slack in the path line of the raw tube is removed;and the raw tube enters in the drawing die without misalignment of theaxis. As a result, occurrence of uneven thickness and buckling areprevented. In terms of the misalignment of the axis of the raw tubeentering the drawing die, the effect of suppressing the misalignment ofthe axis can be obtained by holding the raw tube by both capstans infront of and in back of the drawing die.

The twist angle of the inner spiral grooved tube produced can becontrolled based on the relationship between the drawing speed of theraw tube and the rotation speed of the unwinding side capstan. Under aconstant drawing speed, the higher the rotation speed of the unwindingside capstan, the larger the twist angle.

In the method of producing the inner spiral grooved tube, which is anaspect of the present invention, there is no need to roll the groove byinserting the plug into a round tube as in the groove rolling method.Thus, by forming deep grooves in advance on the inner wall of the rawtube before twisting, the high slim fin type tube, which has a highheight of fins and a narrow apex angle of the fins, can be producedhighly accurately with ease in the method of the present invention. Inaddition, there is no need to clean the inner surface of the tubematerial to remove the residual lubricant oil after processing of theraw tube. Thus, the number of processes can be reduced.

The raw tube on which straight grooves are formed can be easily obtainedby extruding, for example.

In the method of producing an inner spiral grooved tube, which is anaspect of the present invention, a diameter reduction ratio of thedrawing die may be 5% to 40%.

By performing the drawing process and the twisting process at the sametime, the maximum twist angle, which is the twist angle obtainablewithout occurrence of buckling. (hereinafter referred as the twist anglelimit) can be set to a larger value. When only the twisting process isperformed on the raw tubeshear stress is introduced in thecircumferential tangential direction of the raw tube; and the raw tubeis twisted. At that time, compressive stress acts in the longitudinaldirection of the raw tube. The larger the twist angle, the higher thecompressive stress. When this compressive stress exceeds the bucklingstress under which buckling occurs, the tube ended up being buckled.Drawing is effective on reducing this compressive stress by introducingtensile stress in the longitudinal direction by drawing: and theoccurrence of buckling can be suppressed.

In the testing performed by the inventors of the present invention,results, in which the larger the diameter reduction ratio, the moreimproved twist angle limit, are obtained.

If the diameter reduction ratio were too low, the effect of the tensilestress by drawing would be less, making it difficult to obtain a largetwist angle. Thus, it is preferable that the diameter reduction ratio isset to 5% or more. On the other hand, if the diameter reduction ratiowere too high, it would be possible that the raw tube is ruptured. Thus,it is preferable that the diameter reduction ratio is set to 40% orless.

In the method of producing an inner spiral grooved tube, which is anaspect of the present invention, a foremost location, on which the rawtube is wound around the unwinding side capstan; and a foremostlocation, on which the raw tube is sent from the unwinding side capstanto a side of the drawing die, may be displaced in a direction parallelto a rotation axis of the unwinding side capstan for an interspacebetween the unwinding side capstan and the drawing die to be a twistprocessing zone of the raw tube.

In the method of producing an inner spiral grooved tube, which is anaspect of the present invention, forward and backward tension may beintroduced in the raw tube during reducing the diameter of the raw tubewith twisting by passing the raw tube through the drawing die.

In the method of producing an inner spiral grooved tube, which is anaspect of the present invention, the inner spiral grooved tube passingthrough the drawing die may be wound around a drawing side capstan.

In the method of producing an inner spiral grooved tube, which is anaspect of the present invention, the inner spiral grooved tube unwoundfrom the drawing side capstan may be shaped into a form with a seconddrawing die.

In the method of producing an inner spiral grooved tube, which is anaspect of the present invention, the raw tube unwound from the drum maybe shaped into a perfect circle shape with the drawing die before theraw tube reaches to the unwinding side capstan.

In the method of producing an inner spiral grooved tube, which is anaspect of the present invention, the raw tube may be an extruded rawtube made of aluminum or aluminum alloy.

Other aspect of the present invention is an apparatus for producing aninner spiral grooved tube including: a drum holding a raw tube, on aninner surface of which multiple straight grooves along a longitudinaldirection of the raw tube are formed with an interval in acircumferential direction; an unwinding side capstan unwinding the rawtube unwounded from the drum while the unwounded raw tube is woundedaround the unwinding side capstan; a rotation part rotating the drum andthe unwinding side capstan centering on a central axis perpendicular toa winding shaft of the drum; and a drawing die reduces a diameter of theraw tube and introduces twist on the raw tube by passing the raw tubeunwound from the unwinding side capstan thorough the drawing die.

In the apparatus for producing an inner spiral grooved tube, which isother aspect of the present invention, a foremost location, on which theraw tube is wound around the unwinding side capstan; and a foremostlocation, on which the raw tube is sent from the unwinding side capstanto a side of the drawing die, may be displaced in a direction parallelto a rotation axis of the unwinding side capstan for an interspacebetween the unwinding side capstan and the drawing die to be a twistprocessing zone of the raw tube.

In the apparatus for producing an inner spiral grooved tube, which isother aspect of the present invention, the apparatus may be configuredto introduce backward tension in the raw tube on a side in front of thedrawing die by restricting rotation of the drum.

In the apparatus for producing an inner spiral grooved tube, which isother aspect of the present invention, the apparatus may be configuredto introduce forward tension in the inner spiral grooved tube byunwinding the inner spiral grooved tube by winding the inner spiralgrooved tube on a side after the drawing die.

The apparatus for producing an inner spiral grooved tube, which is otheraspect of the present invention, may further includes a second drawingdie shapes the inner spiral grooved tube on a side after the drawingside capstan.

The apparatus for producing an inner spiral grooved tube, which is otheraspect of the present invention, may further includes a drawing dieshaping the raw tube into a perfect circle shape on a side before theunwinding side capstan.

If a capstan were provided in each of the front and the back of thedrawing die; and the raw tube were wound around each capstan, thecentral axis of the processing zone introducing twist could be displacedin the direction parallel to the rotation axis of the capstan from thewinding shaft of the drum or the like to the extent corresponding to thenumber of turns of the tube wound around the capstan. In addition, thedistance of the processing zone of the raw tube could be set from thetop location of the unwinding side capstan to the terminal end portionof the drawing die, and could be controlled to a constant value. At thesame time, there would be no rotation of the inner spiral grooved tubeafter the terminal end portion of the drawing die since the inner spiralgrooved tube is wound around and held on the unwinding side capstan.Thus, there is no abrasion scratch between the inner spiral groovedtubes since the raw tube can be wound around the winding drum withoutrotation.

In addition, in the apparatus for producing an inner spiral groovedtube, which is other aspect of the present invention, each of theunwinding side capstan and the drawing side capstan may be provided witha driven roller, which is configured to be wrapped around by the rawtube or the inner spiral grooved tube in such a way that the raw tube orthe inner spiral grooved tube hangs around the driven roller between:the each of the unwinding side capstan and the drawing side capstan; andthe driven roller, and the driven roller may be placed on a locationwithdrawn from a travel lane of the raw tube or the inner spiral groovedtube.

By arranging the driven roller withdrawn from the travel lane, thetwisting processing zone between capstans can be set in a shortdistance. Thus, occurrence of buckling can be suppressed effectively.

When the driven roller is provided, overlapping of each of the raw tubescould be prevented if it were arranged in the intersecting direction tothe central axis of the capstan. As a result, formation of the surfacescratch; rupturing; and occurrence of buckling on the produced innerspiral grooved tube can be suppressed effectively.

Advantageous Effects of Invention

According to the present invention, the raw tube used is not limited toone made of aluminum alloy particularly; and can be used for one made ofother metal such as copper alloy and the like. In the present invention,the inner grooves of raw tube, which has grooves on the inner surface,such as the electric weld tube and the like, can be used. In theelectric weld tube and the like, an extruded material or a platematerial on which grooves are formed by pressing is processed into around shape by the roll forming process and the junctions are welded.Thus, the degree of freedom and the dimensional accuracy of the shape ofinner surface grooves of the produced inner spiral grooved tube arehigh.

In addition, an inner spiral grooved tube having a high height of finsand a narrow apex angle of the fins can be obtained. Furthermore, thepresent invention can be applied to a fine tube (thinning); and a largetwist angle of 35° or more can be introduced.

These effects are attributed to abilities of: setting the region, inwhich the twisting process in the longitudinal direction of the raw tubeis loaded, short by passing the raw tube through the drawing die afterhaving the unwinding side capstan revolve first; and overlapping thetwist processing zone and the diameter reduction processing zone to theprocessing zone of the drawing die as much as possible.

In addition, the raw tube can reach to the drawing die withoutintroducing twist to the raw tube in the interposing part between thedrum and the unwinding side capstan by synchronously rotating both of:the drum unwinding the raw tube; and the unwinding side capstan with therevolving raw tube, around the same axis to unwind the raw tube to theside of the drawing die. Thus, the twist processing and the diameterreduction processing of the raw tube can be performed while buckling ofthe raw tube is suppressed.

Furthermore, there is no chip formation, such as the aluminum chip andthe like, on the inner surface of the produced inner spiral groovedtube. Thus, the twist angle, the height of fins, and the bottom wallthickness are stable in the longitudinal direction.

Therefore, it does not have an adverse effect on expansion of the tubein assembling of the heat exchanger.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view showing an embodiment of the apparatus forproducing an inner spiral grooved tube according to the presentinvention.

FIG. 2 is an explanatory diagram showing an enlarged main part of theproduction apparatus.

FIG. 3 is a plan view schematically showing the winding state of the rawtube with respect to the unwinding side capstan of the productionapparatus.

FIG. 4 is a cross-sectional view of the drawing die used in theproduction apparatus.

FIG. 5A is a front view showing the raw tube having straight groovesformed on its inner surface.

FIG. 5B is a side sectional view showing the raw tube having straightgrooves formed on its inner surface.

FIG. 6 is an explanatory view showing a cross section and a partlyunfolded state of the tube with the inner spiral grooves in which spiralgrooves are formed on the inner surface.

FIG. 7A is a side view showing an example of a heat exchanger having thetube with the inner spiral grooves according to the embodiment.

FIG. 78 is a perspective view showing an example of a heat exchangerhaving the tube with the inner spiral grooves according to theembodiment.

FIG. 8 is a graph showing the relationship between the distance of theprocessing zone and the twist angle limit when the inner spiral groovedtube is produced in Example of the present invention.

FIG. 9 is a graph showing the relationship between the diameterreduction ratio in drawing and the twist angle limit when the innerspiral grooved tube is produced in Example of the present invention.

FIG. 10 is a graph showing the relationship between the rotation speedof the unwinding side capstan and the twist angle when the inner spiralgrooved tube is produced in Example of the present invention.

FIG. 11 is a graph showing the relationship between the measurementlocation in the longitudinal direction and the twist angle in an exampleof the inner spiral grooved tube produced in Example of the presentinvention.

FIG. 12 is a view showing the apex angle of the fin and the top width ofthe in in the inner spiral grooved tube produced in Example of thepresent invention.

FIG. 13 is an explanatory view showing the inclination angle of the inin the inner spiral grooved tube produced in Example of the presentinvention.

FIG. 14 is a configuration diagram showing an example of a conventionalapparatus for producing an inner spiral grooved tube using a drawingdie.

FIG. 15 is a cross-sectional view of the apparatus for carrying out thegroove rolling method.

FIG. 16 is a configuration diagram showing an example of an apparatusfor producing an inner spiral grooved tube by winding and extruding theextruded raw tube around the outer periphery of a drum.

DESCRIPTION OF EMBODIMENTS

Embodiments of the apparatus for producing an inner spiral grooved tuberelated to the present invention and the method of producing an innerspiral grooved tube using the apparatus are explained below in referenceto the drawings.

The production apparatus A for the inner spiral grooved tube of thepresent embodiment is an apparatus producing the inner spiral groovedtube 11R (FIG. 6) having the spiral grooves on the inner surface byintroducing a constant twist on the raw tube 11 (refer FIGS. 5A and 5B),on the inner surface of which multiple straight grooves 11 a along thelongitudinal direction are formed with an interval in thecircumferential direction.

As shown in FIG. 1, the production apparatus A includes: the drum 21holding the raw tube 11, on the inner surface of which fins 11 b areformed by the straight grooves 11 a, in the state where the raw tube 11is wound in the coiled shape; the unwinding side capstan 22, whichunwinds the raw tube 11, while the raw tube 11 unwound from the drum 21is wound around the unwinding side capstan 22; the rotation part 23rotating the drum 21 and the unwinding side capstan 22 around thecentral axis C perpendicular to the winding shaft 21 a of the drum 21;the drawing die 24, through which the raw tube 11 fed from the unwindingside capstan 22 passes; the drawing side capstan 25 feeding out theinner spiral grooved tube 11R, in which the straight grooves on theinner surface became spiral grooves by passing through the drawing die24 while the inner spiral grooved tube 11R is wound around the drawingside capstan 25; the second drawing side die 26, through which the innerspiral grooved tube 11R having gone through the drawing side capstan 25passes; the third capstan 27 around which the inner spiral grooved tube11R having gone through the second drawing side die 26 is wound; and thewinding drum 29 winding the inner spiral grooved tube 11R, which isunwound from the third capstan 27, around.

The drum 21 on the unwinding side (hereinafter referred as the unwoundside drum) is mounted on the first frame 32 with the guide pulley 31,which guides the unwound raw tube 11 along the central axis C. and thesupport shaft 31 a. In this setup, the unwound side drum 21 is supportedrotatably by the first frame 32 and feeds out the raw tube 11 with aconstant tension controlling the braking force by the winding diameter.The reference symbol 33 indicates the cover enclosing the unwound sidedrum 21, the guide pulley 31 and the like on the whole. In the structureshown in FIG. 1, the braking force of the drum 21 is generated by thebraking device 15 such as the powder brake or the like, which isprovided so as to be connected to the rotation axis 21 a and capable ofadjusting the torque freely

The front end portion 34 and the read end portion 35 of the first frame32 extend along with the central axis C axially. The front end portion34 and the read end portion 35 are supported horizontally and rotatablyaround the central axis by the pair of the leg parts 37 through thebearings 36 for the first frame 32 to be rotatable. The front endportion 34 of the first frame 32 protrudes from the leg part 37 in theforward direction; and the second frame 38, which holds the unwindingside capstan 22, is fixed on the protruding portion. Therefore, thesecond frame 38 is kept in the state where it is fixed on the firstframe 32, and rotatably supported around the central axis C along withthe unwinding side capstan 22.

The first frame 32 includes: the main frame 32 a, which supports therotation axis 21 a of the drum 21 and is in a rectangular frame shape;the sub frame 32 b in an isosceles shape extendedly formed in atapered-off shape from a side of the main frame 32 a in the side view:the front end portion 34 in an axis shape extendedly formed on the frontend side of the sub frame 32 b; and the read end portion 35 in an axisshape extendedly formed on the rear end side of the main frame 32 a.

The front end portion 34 of the first frame 32 protrudes further fromthe other leg part 37 in the forward direction; and the second frame(unwinding side fame) 38 which holds the unwinding side capstan 22, isfixed on the protruding portion. Therefore, the second frame 38 isintegrated to the first frame 32, and rotatably supported around thecentral axis centering on the horizontal central axis C along with theunwinding side capstan 22.

The rear end portion 35 of the first frame 32 protrudes from the legpart 37 in the backward direction; and the drive unit 39 such as a motorand the like is provided below the protruding portion. An end of thetransmission part 39 a such as the endless belt or the like is wrappedaround on the rotation shaft of the drive unit 39: and the other end ofthe transmission part 39 a is wrapped around on the protruding portionof the rear end portion 35. Because of this, the rotation force of therotation shaft of the drive unit 39 is transmitted to the protrudingportion of the rear end portion 35; and the first frame 32 and thesecond frame 38 can be rotated.

Thus, it is configured that the first fame 32 and the second frame 38are rotated as a single piece by the drive unit 39. The rotation part23, which rotates the unwound side drum 21 and the unwinding sidecapstan 22 as a single piece around the central axis C, is constructedfrom: the drive unit 39; the first and second frames 32, 38; thebearings 36; the leg parts 37; and the like.

In the example shown in the drawing, the unwinding side capstan 22 hasthe driven roller 41. The unwinding side capstan 22 re-feeds the rawtube 11 along the central axis C in the state where the raw tube 11 iswound around the unwinding side capstan 22 so as the raw tube 11 to bewrapped around several turns between the unwinding side capstan 22 andthe driven roller 41. The raw tube 11 is fed out along the central axisC1 (the central axis of the processing zone, which is described later),which is displaced from the unwinding track from the unwound side drum21 in the direction parallel to the rotation axis of the capstan 27 asshown in FIG. 3, by being wound around the capstan 22 several turns.Since the raw tube 11 is wound around several turns, the raw tube 11 isunwound from the capstan 22 with a stable tension.

FIG. 2 is a drawing mainly depicting the relative relation of: theunwinding side capstan 22 and the drawing side capstan 25, which areprovided in front of or in back of the drawing die 24; and the raw tube11, among the production apparatus A shown in FIG. 1. Thus, depiction ofthe driven rollers 41, 43 is omitted in FIG. 2.

In addition, the processing zone is defined as the distance L, which isthe distance between the top portion of the capstan 22 and the exit partof the drawing die 24, as shown in FIG. 2.

In this case, the driven roller 41 is provided in the location withdrawnfrom the central axis C (traveling track of the raw tube 11). In theexample shown in the drawing, the driven roller 41 is arranged to bevertical to the central axis C (traveling track of the raw tube 11) fromthe unwinding side capstan 22. In addition, the capstan 22 and thedriven roller 41 are not arranged in parallel; and the central shaft ofthe driven roller 41 is arranged in the direction intersecting with thedirection of the central shaft of the capstan 22. By being arrange inthis way, overlapping of the pieces of the raw tube, which are woundaround them, can be prevented. Thus, formation of the surface scratch;rupturing; and occurrence of buckling on the produced inner spiralgrooved tube can be suppressed effectively.

In addition, the production apparatus A includes the drawing die 16,which recovers the roundness on the raw tube 11 before the twistprocessing, in the bearing 36 in the leg part 37.

The raw tube 11 wound in the coiled shape is deformed in a flat shapedue to contacting with each of raw tubes. When drawing is performed inthe deformed shape, the flat raw tube 11 does not contact with thedrawing die 24 evenly, and is buckled by introduction of twist. Thus,drawing in 0.5% to 3% of the dimension reduction ratio is performed inorder to obtain the circularity, in which the short diameter/longdiameter ratio is L2 or less. The diameter reduction ratio can beobtained from the percentage of ((the outer diameter of the raw tube 11before drawing)−the outer diameter of the inner spiral grooved tubeafter drawing))(the outer diameter of the raw tube 11 before drawing).

The drawing die 24 is provided above the central axis C1 in such a waythat the raw tube 11 immediately after being unwound from the unwindingside capstan 22, passes through the drawing die 24. Specifically, thedrawing side capstan 25 is arranged in the state where the unwindingside capstan 22 and the traveling track of the raw tube 11 are alignedto the central axis C1; and the drawing die 24 is provided between thecapstans 22, 25. The drawing side capstan 25 rotates by motor drive. Inthis setup, the drawing side capstan 25 is supported by the table 42.The drawing die 24 is fixed on the front end portion of the table 42integrally.

The drawing side capstan 25 has the driven roller 43 similar to theunwinding side capstan 22. The drawing side capstan 25 feeds the rawtube 11 in the direction parallel to the central axis C1 in the statewhere the inner spiral grooved tube 11R is wound around the drawing sidecapstan 25 so as the inner spiral grooved tube 11R to be wrapped aroundseveral turns between the drawing side capstan 25 and the driven roller43.

The inner spiral grooved tube 11R is wound around the drawing sidecapstan 25 several turns. The inner spiral grooved tube 11R is fed tothe drawing side capstan 25 displaced from the central axis C betweenthe capstans 22, 25 in the direction parallel to the rotation shaft ofthe capstan 25

As in the case in the unwinding side capstan 22, the driven roller 43 isprovided in the location withdrawn from the central axis C1 (travelingtrack of the inner spiral grooved tube 11R) too. The driven roller 43 isarranged to be vertical to the central axis C1 (traveling track of theinner spiral grooved tube 11R) from the drawing side capstan 25. Thus,the distance between the drawing side capstan 25 and the unwinding sidecapstan 22 in the upstream is shortened; and the twist processing zonein between becomes short. As a result, occurrence of buckling on theproduced inner spiral grooved tube 11R can be suppressed effectively.

The drawing die 24 has the die hole 42 a, through which the raw tube 11passes, as shown in FIG. 4; and empty drawing for reducing the outerdiameter of the raw tube 11 is performed. The diameter reduction ratioin the drawing die 24 is set to 5% to 40%. If the diameter reductionratio were too low, the effect obtained by drawing would beinsufficient, making it difficult to obtain a large twist angle. Thus,it is preferable that the diameter reduction ratio is 5% or more. On theother hand, if the diameter reduction ration were too high, rupturing ofthe tube would be likely to occur due to exceeding the processing limit.Thus, it is preferable that the diameter reduction ratio is 40% or less.

In the present embodiment, the third capstan 27, which is supported bythe table 44, is provided on the location downstream to the drawing sidecapstan 25. The second drawing die 26 is provided between the drawingside capstan 25 and the third capstan 27. The third capstan 27 rotatesby motor drive. The second drawing die 26 is provide for skin passing ofthe inner spiral grooved tube 11R, which is produced by being passedthrough the drawing dice 24 in the previous step. The change of thedimension reduction ratio in the second drawing die 27 is less. Bypassing through the second drawing die 27, the surface and the dimensionare subjected to the finishing shaping; and the roundness of the innerspiral grooved tube 11R is recovered.

The third capstan 27 is configured similar to the above-described othercapstans 22, 25. The inner spiral grooved tube 11R is unwound in thestate where the inner spiral grooved tube 11R is wound around the thirdcapstan 27 so as t the inner spiral grooved tube 11R to be wrappedaround several turns between the third capstan 27 and the driven roller45. The driven roller 45 is configured similar to the other drivenrollers 41, 43 in that: the driven roller 45 is arranged displaced fromthe central axis C (traveling track of the raw tube 11); and the drivenroller 45 is arranged to be vertical to the central axis C (travelingtrack of the raw tube 11) from the third capstan 27.

The winding drum 29 is for winding the inner spiral grooved tube 11Rwith a constant tension, and has the drive unit 46 for its rotation.

Next, the method of producing the inner spiral grooved tube 11R by usingthe production apparatus A configured as described above is explained.

The raw tube 11, on the inner surface of which multiple straight grooves11 a along the longitudinal direction are formed with an interval in thecircumferential direction, is produced by extrusion in advance as shownin FIG. 4 (the raw tube extruding process).

Then, the raw tube 11 is held on the unwound side drum 21 in the coiledshape. The raw tube 11 is unwound from the unwound side drum 21 rotatingthe raw tube 11 by rotating the unwound side drum 21 and the unwindingside capstan 22 around the central axis C along with the frames 32, 38by the rotation part 23 while the raw tube 11, which is unwound from theunwound side drum 21, is wound around the unwinding side capstan 22 (theraw tube unwinding process).

The diameter of the raw tube 11 is reduced by performing the drawingprocessing by winding the raw tube 11 around the drawing side capstan 25after the unwound raw tube 11 passes the drawing die 24 (the raw tubedrawing process). By the raw tube drawing process, twist is introducedin the raw tube 11; and it is turned into the inner spiral grooved tube11R, on the inner surface of which spiral grooves are formed.

In this case, shearing stress is placed on the raw tube 11 in thecircumferential tangential direction by twisting to introduce the twistangle. Simultaneously, compressive stress accompanying the twist isplaced in the longitudinal direction of the raw tube 11. When the valueof the compressive stress exceeds the buckling stress, buckling occurs.However, the compressive stress can be reduced by the tensile stress inthe longitudinal direction of the raw tube in the drawing process. Thus,occurrence of buckling can be suppressed.

The raw tube 11 or traveling track of the raw tube 11 is wound aroundeach of the capstans 22, 25 provided in front of and in back of thedrawing die 24. Thus, the central axis C1 of the processing zoneintroducing twist is displaced from the winding shaft of the drum andthe winding shaft of the final winding drum in the direction parallel tothe rotation axis of the capstan 22 from the winding shaft of the drumor the like to the extent corresponding to the number of turns of thetube 11 wound around the unwinding side capstan 22. In addition, by theraw tube 11 being wound around and held on the capstans 22, 25 in frontof and in back of the drawing die 24, the distance of the processingzone of the raw tube 11 is defined as the distance L: from the toplocation of the unwinding side capstan; to the terminal end portion ofthe drawing die, as shown in FIG. 4, the distance L can be controlled toa constant value. The longer the processing zone, the smaller thebuckling stress. Thus, when the processing zone is long, buckling islikely to occur even in a small twist angle introduction. By adjustingthe distance between the capstans 22, 25 and setting the distance asshort as possible, occurrence of buckling can be suppressed even inintroducing a large twist angle.

If the location of the drawing side capstan 25 were too far away fromthe terminal end portion of the drawing die 24, the force holding theinner spiral grooved tube 11R would become low even if it is woundaround the capstan 25; and the inner spiral grooved tube 11R wouldrotate even after passing through the drawing die 24. In this case, thedistance of the processing zone in the longitudinal direction varies,causing variation of the twist angles in the longitudinal direction.

If the distance between both capstans 22, 25 were set too narrow, thecapstans 22, 25 would contact the table 42 supporting the drawing die24. Thus, it is preferable that the distance is set to narrow but in therange being able to avoid the contact between the capstans 22, 25 andtable 42. It is preferable that the diameters of both capstans 22, 25are set to 100 mm or more. If they were less than 100 mm, it would bepossible that the raw tube is buckled or flattened in winding aroundeach of both capstans 22, 25. On the other hand, if they were 900 mm ormore, it would be possible that buckling occurs due to too wide distancebetween the capstans 22, 25, as explained above.

The twist angle of the inner spiral grooved tube is set based on therelationship between the rotation speed of the unwinding side capstan 22and the unwinding speed of the raw tube 11.

The surface of the inner spiral grooved tube 11R is subjected to thefinishing shaping by unwinding the inner spiral grooved tube 11R formedby the drawing process from the drawing side capstan 25; and insertingthe inner spiral grooved tube 11R into the second drawing die 26 betweenthe both capstans 25, 27 while the inner spiral grooved tube 11R iswound around the third capstan 27 (the finishing drawing process). Evenin the case where deformation, such as some collapse and the like, wasformed on the inner spiral grooved tube 11R in the raw tube drawingprocess, by going through this finishing drawing process, thedeformation can be corrected to obtain the inner spiral grooved tube 11Rhaving a predetermined roundness.

Finally, the inner spiral grooved tube 11R is wound around the windingdrum 29 (the winding process).

The winding drum 29 rotates by motor drive synchronizing with thedrawing side capstan 25 and the capstan 27.

As described above, the inner spiral grooved tube 11R having a largetwist angle can be produced without occurrence of buckling by performingthe drawing process rotating the raw tube 11 in the state where aconstant tension is placed between the unwinding side capstan 22 and thedrawing side capstan 25. Particularly, there is no need to perform thegroove rolling method, in which the plug or the like is inserted inside.Thus, by forming the fins 11 b having a high height and a narrow apexangle on the inner surface of the raw tube 11 in extrusion work inadvance, the raw tube 11 can be twisted without crushing the fins 11 b.In addition, the slim fin type inner spiral grooved tube 11R can beproduced; and there is no need for cleaning the inner surface of thetube material after the processing particularly.

FIGS. 7A and 7B are schematic drawings showing an example of the heatexchanger 80 having the inner spiral grooved tube 11R related to thepresent invention. The heat exchanger 80 has the structure in which theinner spiral grooved tube 81 is provided meanderingly as the tube forrunning the refrigerant; and multiple fin materials 82 made of aluminumalloy are provided in parallel around the inner spiral grooved tube 81.The inner spiral grooved tube 81 is provided so as to pass through themultiple through holes, which are provided to penetrate through the finmaterials 82 provided in parallel.

In the structure of the heat exchanger 80 shown in FIGS. 7A and 7B, theinner spiral grooved tube 81 is made by connecting adjacent end openingsof adjacent multiple U shaped main tubes 81A, which penetrate throughthe fin materials 82 in a straight shape, with the U shaped elbow tube81B each other as shown in FIG. 7B. The heat exchanger 80 shown in FIGS.7A and 7B is configured by having: the inlet of refrigerant 86 formed onan end side of the inner spiral grooved tube 81 penetrating through thefin materials 82; and the outlet of refrigerant 87 formed on the otherend side of the inner spiral grooved tube 81.

The heat exchanger 80 shown in FIGS. 7A and 7B is assembled bymechanically integrating the inner spiral grooved tube 81 and the finmaterials 82 by: providing the inner spiral grooved tube 81 so as topenetrate through the through holes formed in each of the fin materials82; and expanding the outer diameter of the inner spiral grooved tube 81by an expansion plug after having them penetrate through the throughholes of the fin materials 82.

By adapting the inner spiral grooved tube 81 to the heat exchanger 80shown in FIGS. 7A and 7B, the heat exchanger 80 having excellent heatexchange efficiency can be provided.

In addition, for example, when the heat exchanger 80 is configured byusing the inner spiral grooved tube 11R, which has a narrow outerdiameter of 10 mm or less and is made of aluminum or aluminum alloy, thedown-sized high-performance heat exchanger with excellent recyclabilitycan be provided, since there is no need for the fin materials 82 and theinner spiral grooved tube 81 to be separated in recycling process.

EXAMPLES Example 1

The inner spiral grooved tube was produced by using the raw tube made of3003 aluminum alloy, on the inner surface of which straight grooveshaving the dimension of: 10 mm of the outer diameter; and 9.1 mm of theinner diameter, were formed.

As the raw tube, the extruded material made of 3003 aluminum alloy andhaving the dimension of: 10 mm of the outer diameter; and 9.1 mm of theinner diameter, was used as it was extruded. The number of straightgrooves on the inner surface was 45 (8°/a protrusion). The height of thefins formed by these straight grooves was 0.28 mm: and the apex angle ofthe fins was 10°. By using this raw tube, the drawing process wasperformed in the condition of: 7.5 mm of the pore size of the drawingdie; 25% of the diameter reduction ratio; and 5 m/min of the drawingspeed.

First, the distance of the processing zone and the rotation speed of theunwinding side capstan were increased to investigate their relationshipwith the twist angle limit (the maximum twist angle without occurrenceof buckling); and results shown in FIG. 9 were obtained.

As shown in FIG. 8, there was correlation between them. It showedtendency that the value of the twist angle limit was increasedexponentially accompanying with decrease of the distance of theprocessing zone. When the distance of the processing zone was 180 mm,buckling did not occur, which was a reference data.

The inner spiral grooved tube, which was produced in the above-describedcondition with the processing zone length of 220 mm, had: the outerdiameter of 7.5 mm; and the spiral grooves formed on the inner surfacewith the twist angle of 30° after the raw tube drawing process. Afterthe finish drawing process, the twist angle became a bit smaller bypassing through the third drawing die, and ended up with the outerdiameter being 7.7 mm and the twist angle of the inner spiral groovebeing 28° in the end.

In addition, the rotation speed of the unwinding side capstan waschanged; and effects of the diameter reduction ratio during drawing onthe twist angle limit (the maximum twist angle without occurrence ofbuckling) were investigated in the condition of: 220 mm of theprocessing zone distance; and 5 m/min of the drawing speed, by using theraw tube made of 3003 aluminum alloy with the outer diameter of ϕ10 andthe inner diameter of ϕ9.1, on the inner surface of which straightgrooves were provided. Results shown in FIG. 9 were obtained.

As shown in FIG. 9, there was correlation between them. It showedtendency that the twist angle limit was increased accompanying withincrease of the diameter reduction ratio in drawing.

Next, the relationship between the twist angle in drawing and therotation speed of the frame on the unwinding side was investigated byusing: the extruded raw tube made of 3003 aluminum alloy with the outerdiameter of ϕ=10 mm and the inner diameter of ϕ=9.1 mm, on the innersurface of which straight grooves were provided; and the apparatus shownin FIG. 1. Results shown in FIG. 10 were obtained.

FIG. 10 shows the relationship between the twist angle and the rotationspeed of the unwinding side capstan in the condition of: 220 mm of theprocessing zone distance; 30% of the diameter reduction ratio; ϕ7.5 mmof the outer diameter, ϕ6.6 mm of the inner diameter; and the 10 m/minof the drawing speed.

The rotation speed of the unwinding side frame and the twist angle hadproportional relationship. It was demonstrated that the twist angelcould be modulated by changing the rotation speed of the unwinding sideframe

Example 21

Next, the inner spiral grooved tube having the inner spiral grooves of20° in the length of 778 m was produced in the production condition of:220 mm of the processing zone distance: 30% of the diameter reductionratio; 10 m/min of the drawing speed; 180 rpm of the rotation speed ofthe unwinding side capstan; ϕ7.5 mm of the outer diameter; and ϕ6.6 mmof the inner diameter, by using: the raw tube made of 3003 aluminumalloy with the outer diameter of ϕ=10 mm and the inner diameter of ϕ=9.1mm, on the inner surface of which straight grooves were provided; andthe apparatus shown in FIG. 1. A part of the inner spiral grooved tubewas cut out in the length of 5 m; and distribution of the twist anglesin the longitudinal direction of the cut out inner spiral grooved tubewas investigated. Results shown in FIG. 11 were obtained.

Based on the results shown in FIG. 11, it was demonstrated that thetwist angel was introduced stably in the longitudinal direction in theinner spiral grooved tube formed by using the production apparatus shownin FIG. 1. In addition, the variety of the twist angles was kept in therange of plus and minus 0.5%, demonstrating that the twist angle wasintroduced evenly in the longitudinal direction of the tube material inan extremely high accuracy.

Example 31

Next, the inner spiral grooved tube having the inner spiral grooves of25° in the length of 778 m was produced by using: the raw tube made of3003 aluminum alloy with the outer diameter of ϕ=10 mm and the innerdiameter of ϕ=9.0 mm, on the inner surface of which straight grooveswere provided; and the apparatus shown in FIG. 1. The production wasperformed in the condition of: 30% of the diameter reduction ratio 220mm of the processing zone distance; 47 mm of the outer diameter; 10m/min of the drawing speed; and 250 rpm of the rotation speed of theunwinding side capstan.

On the inner spiral grooved tube having the length of 778 m, the twistangle (°); the outer diameter (mm); the bottom wall thickness (mm): theheight of the fin (mm); the top width of the fin (mm); and the apexangle of the fin (°) were measured at each of locations 10 m, 195 m, 389m, 584 m, and 775 m from the start point of the processing in thelongitudinal direction. Results are shown in Table 1.

The apex angle of the fin is the angle made by two hypotenuses on theright and the left in the fin in the isosceles shape shown in FIG. 12.The top width of the fin is the width of the fin on the top part of thefin. The height of the fin is the height from the bottom part of the finto the top part of the fin.

The bottom wall thickness is the wall thickness of the inner spiralgrooved tube 11R corresponding to the part of the spiral groove 11 d asshown in FIG. 13. The inner spiral grooved tube 11R has a circular crosssection. Thus, strictly speaking, the height of the fin was measured asthe height t between the midpoint of the bottom side of the fin 11 c andthe midpoint of the top side of the fin 11 c as shown in FIG. 13.

In addition, TS (tensile strength), YS (proof strength), and EL(elongation) were measured by cutting out a part of the obtained innerspiral groove tube at each of locations in the length of 140 mm andusing the cut out tubes as the testing pieces directly.

TABLE 1 Bottom Top Apex Twist Outer wall Height of width of angle ofMeasurement angle diameter thickness the fin the fin the fin TS YS ELlocation (°) (mm) (mm) (mm) (mm) (°) (MPa) (MPa) %( ) Target value 25 70.5 0.21 0.11 15 — — — 10 m 25.5 7.02 0.504 0.214 0.108 15.5 174 152 6.9195 m 24.8 7.01 0.496 0.208 0.107 15.8 174 153 6 389 m 25.3 7.04 0.4950.212 0.109 14.8 70 151 5.7 584 m 24.9 6.98 0.505 0.212 0.113 14.9 172154 6.2 775 m 25 7.02 0.505 0.21 0.115 15.7 169 150 5.8

From the results shown in Table 1, it was demonstrated that the innerspiral grooved tube produced by the apparatus shown in FIG. 1 had:longitudinally even twist angle; the outer diameter; the height of thefin; the top width of the fin: and the apex angle of the fin, even itwas the inner spiral grooved tube having the length of about 778 m. Interms of the twist angle, it was within plus and minus 0.5% relative tothe targeted angle of 25°.

In addition, varieties of TS, YS, and EL in the obtained inner spiralgrooved tube were small; and it was demonstrated that it was processedevenly.

The present invention is not limited by the descriptions of theembodiments. In terms of the material, it is not limited particularly toaluminum alloy, can be used for copper alloy and the like. The presentinvention can be modified in many ways without deviating from the scopeof the present invention.

INDUSTRIAL APPLICABILITY

According to the present invention, a heat transfer tube having an evenhigher performance can be provided at a lower cost. Thus, the presentinvention contributes to: improving the performance; reducing theweight; reducing the cost; and the like of a heat exchanger.

REFERENCE SIGNS LIST

-   -   A: Apparatus for producing an inner spiral grooved tube    -   11: Raw tube    -   11 a: Straight groove    -   11 b: Fin    -   11R: Inner spiral grooved tube    -   21: Drum (unwound side drum)    -   21 a: Winding shaft    -   22: Unwinding side capstan    -   23: Rotation part    -   24: Drawing die    -   24 a: Die hole    -   25: Drawing side capstan    -   26: Second drawing die    -   27: Third capstan    -   29: Winding drum    -   31: Guide pulley    -   32: Frame (first frame)    -   38: Second frame    -   C: Central axis (central axis of the rotation part)    -   C1: Central axis (central axis of the processing zone)

What is claimed is:
 1. A method for producing an inner spiral groovedtube comprising the steps of: twisting and drawing an unwound raw tube,which has grooves or fins on an inner surface, by introducing twist tothe unwound raw tube while a diameter of the unwound raw tube is reducedby being passed through a drawing die, to obtain an inner spiral groovedtube, the unwound raw tube being wound up on an unwinding side capstan;and winding up the inner spiral grooved tube, wherein the unwinding sidecapstan rotates in such a way that: apost-unwound-pre-diameter-reduction raw tube from having been unwoundfrom the unwinding side capstan to reaching to the drawing die rotatesabout a central axis of the post-unwound-pre-diameter-reduction rawtube; and the raw tube before being wound up on the unwinding sidecapstan rotates in synchronization with the raw tube being wound up onthe unwinding side capstan.
 2. The method for producing an inner spiralgrooved tube according to claim 1, wherein a diameter reduction ratio ofthe drawing die is 5% to 40%.
 3. The method for producing an innerspiral grooved tube according to claim 1, wherein a foremost location,on which the raw tube is wound around the unwinding side capstan; and aforemost location, on which the raw tube is sent from the unwinding sidecapstan to a side of the drawing die, are displaced in a directionparallel to a rotation axis of the unwinding side capstan for aninterspace between the unwinding side capstan and the drawing die to bea twist processing zone of the raw tube.
 4. The method for producing aninner spiral grooved tube according to claim 1, wherein forward andbackward tension are introduced in the raw tube during reducing thediameter of the raw tube with twisting by passing the raw tube throughthe drawing die.
 5. The method for producing an inner spiral groovedtube according to claim 1, wherein the inner spiral grooved tube passingthrough the drawing die is wound around a drawing side capstan.
 6. Themethod for producing an inner spiral grooved tube according to claim 5,wherein the inner spiral grooved tube unwound from the drawing sidecapstan is shaped into a form with a second drawing die.
 7. The methodfor producing an inner spiral grooved tube according to claim 1, whereinthe raw tube unwound from the drum is shaped into a perfect circle shapewith the drawing die before the raw tube reaches to the unwinding sidecapstan.
 8. The method for producing an inner spiral grooved tubeaccording to claim 1, wherein the raw tube is an extruded raw tube madeof aluminum or aluminum alloy.